Ion implantation is a standard technique for introducing conductivity-altering impurities into a workpiece. A desired impurity material is ionized in an ion source, the ions are accelerated to form an ion beam of prescribed energy, and the ion beam is directed at the surface of the workpiece. The energetic ions in the beam penetrate into the bulk of the workpiece material and are embedded into the crystalline lattice of the workpiece material to form a region of desired conductivity.
In one instance, a ribbon ion beam is used to implant the workpiece. A ribbon ion beam cross-section has a long dimension and a short dimension. The long dimension, for example, may be referred to as a width or x-direction, though other orientations are possible. The ribbon ion beam may be formed using a parallelizing lens or may be a scanned spot beam.
Solar cells are one example of a device that uses silicon workpieces. Any reduced cost to the manufacture or production of high-performance solar cells or any efficiency improvement to high-performance solar cells would have a positive impact on the implementation of solar cells worldwide. This will enable the wider availability of this clean energy technology.
There are many different solar cell architectures. Two common designs are the selective emitter (SE) and the interdigitated backside contact (IBC). A SE solar cell has high-dose stripes across the lightly doped surface impinged by sunlight. An IBC solar cell has alternating p-type and n-type stripes across the surface not impinged by sunlight. Both a SE and IBC solar cell may be implanted to dope the various regions.
Solar cells or other workpieces may need to be implanted such that different regions receive different doses. In most instances, this requires multiple implantation steps. For SE solar cells, one implant is typically a blanket implant across the entirety of the solar cell and the second implant is typically a selective implant into particular regions that need a heavier dose. The selective implant may use, for example, photoresist or a stencil mask. Use of two implants adds processing costs, increases production time, and may increase the number of implanters required in a manufacturing facility. Furthermore, lithography is costly and time-consuming and stencil masks may be difficult to properly align. Therefore, there is a need in the art for patterned implantation and, more particularly, patterned implantation where different doses are implanted simultaneously.